This invention relates to a washing machine incorporating a brushless motor serving as a washing machine motor for driving both a dehydration tub and an agitator.
An agitator is driven by a washing machine motor for either a wash or a rinse operation and a dehydration tub is rotated at a high speed by the washing machine motor for a dehydration operation, as well known in the art. Induction motors have been employed as such a washing machine motor as described above.
Recently, small-sized, light-weight and yet, high-level cleaning performance washing machines have been demanded. To meet this demand, an output torque of the washing machine motor needs to be increased. However, an output power of the induction motor conventionally employed as the washing machine motor is at a relatively low level. Accordingly, in order to obtain a desired output torque from the induction motor, a rating power of the induction motor needs to be increased. However, the increase in the rating power increases the size of the induction motor, which further increases the size of the washing machine. In view of this disadvantage, it has been proposed to employ a brushless motor as the washing machine motor for the induction motor. A brushless motor running system generally comprises a position sensing element for sensing a rotational position of a rotor of the brushless motor and a motor drive control circuit including an inverter main circuit for driving the motor and an inverter control circuit for controlling the inverter main circuit based on a signal generated by the position sensing element so that the motor is driven at a desired rotational speed and a feedback control is performed to obtain a constant speed.
The above-mentioned inverter main circuit includes transistors serving as semiconductor switching elements. These transistors are deteriorated to cause malfunction when an overcurrent due to a heavy load flows into the inverter main circuit. To solve this problem, it has been proposed to detect the overcurrent by detecting the inverter main circuit current. However, in the washing machines, an instantaneous overcurrent flows when the load applied to the motor temporarily varies because of movement of the clothes in the tub. Such an instantaneous overcurrent has little influence upon the transistors. Thus, the instantaneous overcurrent due to the movement of the clothes in the tub can be mistakenly determined to be an overcurrent due to a continuous heavy load causing malfunction of the transistors.
Furthermore, the above-mentioned position sensing element is to be disposed inside the washing machine motor placed at the lower portion of the washing machine while the inverter control circuit is to be arranged at the upper portion or the rear of the washing machine. A long signal line will be necessary between the position sensing element and the inverter control circuit. Noise will be likely to invade the long signal line and consequently, the signal transmission from the position sensing element to the inverter control circuit will become unreliable.